Multiband Adaptive Impedance Compensation Methods for Spatially Robust Capacitive Power Transfer Systems

This study aims to compare the merits of using both adaptive load resistance and adaptive frequency for impedance compensation in capacitive power transfer (CPT) systems. An adaptive load and frequency-band-switching compensation method is presented that achieves spatial robustness in a CPT system. The method complies with spectrum constraints that limit wireless power transfer to the discrete industrial, scientific, and medical (ISM) frequency bands. Coarse impedance control is obtained by switching frequencies, and fine impedance control is obtained by changing load resistance. The method is verified experimentally in a dual-band CPT system operating at two octave-spaced ISM bands: 13.56 and 27.12 MHz. The system is comprised of a six-plate CPT link, class-E inverters, and class-E self-synchronous rectifiers. Adaptive load compensation is implemented at the output of the rectifier. Experimental results show that, with frequency and load compensation, load power can be held constant over a spatial gap that ranges from 4.0 to 16.0 cm. Results show that the dual-band operation extends the spatial bandwidth of the system by 50% compared with a single frequency system operating at 13.56 MHz.